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- ItemSomente MetadadadosDecreased density of binding sites for the Ca2+ channel antagonist [3H] isradipine after denervation of rat vas deferens(Elsevier B.V., 1994-05-02) Jurkiewicz, Aron [UNIFESP]; Lafayette, Simone Sette Lopes [UNIFESP]; Nunes, S. H.; Martini, L. C.; Docarmo, LGD; Wanderley, A. G.; Jurkiewicz, N. H.; Universidade Federal de São Paulo (UNIFESP)Radioligand binding assays were performed with the selective antagonist of dihydropyridine-sensitive Ca2+ channels [H-3]PN200-110 (isradipine) in rat vas deferens, before and 7 days after denervation, and data were compared with those obtained for K+-induced contractions, which are Ca2+-dependent. the density (B-max) of dihydropyridine binding sites was decreased to almost one-third of its normal value after denervation. the respective affinity (K-D) was not significantly changed. in addition, it was observed that the K+-induced tonic contraction, which corresponded to 55 +/- 2% of the respective phasic contraction, was decreased to 41 +/- 3% after: denervation. It is assumed that the decreased density of Ca2+ channels causes a decrease in K+-induced influx of Ca2+ and consequently of the corresponding tonic contraction. These results indicate that autonomic innervation can regulate the density of dihydropyridine-sensitive Ca2+ channels in the rat vas deferens.
- ItemSomente MetadadadosDIFFERENT MECHANISMS OF ACTION OF AGENTS ACTING ON BETA-ADRENOCEPTORS IN BARIUM-STIMULATED AND ELECTRICALLY-STIMULATED RAT VAS-DEFERENS(Stockton Press, 1991-09-01) Diaz-Toledo, Alejandro [UNIFESP]; Jurkiewicz, Aron [UNIFESP].; Universidade Federal de São Paulo (UNIFESP)1 The relaxation induced by beta-adrenoceptor agonists in rat vas deferens was examined under two different experimental conditions: on electrically-induced twitch responses (35 V, 3 ms, 0.07 Hz), and on contractions induced by single doses of barium chloride (300-mu-M). The experiments were performed in vasa of reserpine-treated rats, after blockade of alpha-adrenoceptors and extraneuronal uptake with dibenamine (10-mu-M, 30 min), and neuronal uptake with cocaine (10-mu-M).2 When twitch responses were used, the values of pD2, interpolated from cumulative concentration-response curves for isoprenaline (Iso), adrenaline (Ad), and noradrenaline (NA) showed a rank order of potency consistent with the presence of beta-2-adrenoceptors (Iso > Ad >> NA).3 When twitch responses were used, the non-selective beta-antagonist, propranolol, caused a concentration-dependent parallel shift to the right of Iso concentration-response curves. Similar shifts were obtained by use of the beta-2-antagonist, isopropylmethoxamine (IMA), and higher doses of the beta-1-antagonist, practolol, according to the expectations from receptor occupation theory. Practolol presented the lowest value of pK(B), 5.03, corroborating the presence of beta-2-adrenoceptors.4 When twitch responses were used, and Ad or NA employed instead of Iso, the antagonists produced shifts of concentration-response curves which were smaller than expected from theory, precluding the determination of pK(B) values. This indicates that other mechanisms are involved besides an interaction with a single population of postsynaptic beta-2-adrenoceptors.5 When barium chloride was used instead of twitch responses, although the potencies of Iso and Ad were increased respectively by about 30 fold and 5 fold, the rank order of potency was still consistent with an interaction with beta-2-adrenoceptors. In addition, the antagonists produced parallel and concentration-dependent shifts of the curves of all the agonists, as expected from receptor theory. The values of pK(B) for a given antagonist were not modified by interchanging the agonists used, indicating a typical interaction with a single population of beta-2-adrenoceptors. When compared to the field-stimulated vas, the values of pK(B) for propranolol and IMA against isoprenaline were respectively 1.3 and 0.6 log units larger. These results suggest the beta-adrenoceptor agents act by different mechanisms of action in barium-stimulated and electrically-stimulated vas.6 It is suggested that when barium is used, the effects of agents acting on beta-adrenoceptors are mediated only by postsynaptic beta-2-receptors, while other complicating factors, probably nerve-dependent presynaptic mechanisms, may be involved with electrical stimulation.
- ItemSomente MetadadadosA double perfusion system with 2-channel recording for the simultaneous study of the contractile responses of the circular and longitudinal smooth-muscle layers of the rat vas-deferens(J R Prous Sa, 1990-09-01) Jurkiewicz, Aron [UNIFESP]; Caricati-Neto, Afonso [UNIFESP]; Brito, Alba Regina Monteiro Souza [UNIFESP]; Mulford, Stanley dos Santos; Busatto, Pedro Arnal [UNIFESP]; Universidade Federal de São Paulo (UNIFESP)A device for double perfusion of the vas deferens externally and through the lumen is described in detail. The perfusion system allows the simultaneous recording of drug-induced or spontaneous contractions of the circular and longitudinal smooth muscle layers of the organ. Isometric contractions of the longitudinal (external) layer are recorded through a tension transducer. The contractions of the circular (internal) smooth muscle layer are recorded as changes of the pressure of internal perfusion. Therefore, four different effects can be recorded for a given concentration of agonist by combining the variables related to the route of perfusion (external or internal) and type of muscle (longitudinal or circular). In addition, antagonism or synergism can be studied by simultaneously perfusing a second drug. Results can be expressed as single records or as mean concentration-response curves from which drug-receptor parameters can be directly or indirectly obtained. The importance of employing this method for the analysis of some less usual problems related to the mechanism of drug action is discussed.
- ItemSomente MetadadadosIN VITRO DENERVATION OF THE RAT VAS-DEFERENS THROUGH HYPOTHERMIC STORAGE(Stockton Press, 1992-10-01) Jurkiewicz, Neide Hyppolito [UNIFESP]; Garcia, Antonio G.; Jurkiewicz, Aron [UNIFESP]; Universidade Federal de São Paulo (UNIFESP); UNIV AUTONOMA MADRID1 The rat vas deferens was excised, stored at 4-6-degrees-C and tested after 24, 48, 72 or 96 h for its contractile activity and for the presence of innervation.2 The maximal contractile capacity of the vas, tested through cumulative concentrations of barium chloride (3 x 10(-2) m) was progressively reduced from about 110 mm to about 63 mm after 72 h, without further decay after 96 h. Spontaneous rhythmic contractions were practically absent.3 A loss of endogenous pools of catecholamines was indicated by four parameters: (a) a decline of about 80% after 24 h and of more than 95% after 48 h of the contractile effect of the indirect sympathomimetic agonist tyramine; (b) a fall of about 20%, 50% and 85% on the concentration of noradrenaline, respectively after 24, 48 and 72 h; (c) a fall of about 25% and 90% after respectively 24 and 48 h, of the activity of dopamine-beta-hydroxylase (DBH); (d) a decline of noradrenaline-induced histofluorescence on cross sections of the vas.4 A loss of neuronal uptake capacity was indicated by: (a) a progressive variation of the apparent affinity for adrenaline, expressed as pD2 values, that increased by about 1.5 log units (corresponding to a 30 fold potentiation) after 72 h, and (b) a reduction of the ability of cocaine to potentiate the contractile effects of adrenaline.5 The pD2 values for barium chloride, 5-hydroxytryptamine (5-HT) and histamine were not significantly changed, while the corresponding value for acetylcholine was slightly but significantly reduced by about 0.8 log units.6 The maximal heights of concentration-response curves for noradrenaline, acetylcholine, histamine and 5-HT were reduced by 42-66% in relation to controls. However, when this reduction was measured in relation to the corresponding barium effect, by means of the relative responsiveness ratio (rho), a small though significant increase was observed for noradrenaline, and a fall for the other drugs.7 It is concluded that: (1) the values for the various biochemical and pharmacological parameters decline at different rates, though revealing altogether that denervation is completed by at least 85% after 72 h of hypothermic storage; (2) two of the results, i.e., the lack of spontaneous rhythmic contractions and the lack of increased contractile effects for acetylcholine, 5-HT and histamine, indicate that in these conditions the vas is devoid of the so-called nonspecific sips of denervation.
- ItemSomente MetadadadosIncreased density of alpha-adrenoceptors in vas-deferens of spontaneously hypertensive rats (SHR), indicated by functional and receptor-binding studies(Elsevier B.V., 1992-07-21) Caricati-Neto, Afonso [UNIFESP]; Sette, M.; Jurkiewicz, A.; Universidade Federal de São Paulo (UNIFESP)Pharmacological parameters were determined from contractile responses mediated by alpha-adrenoceptors in vas deferens from spontaneously hypertensive rats (SHR) and corresponding normotensive controls, Wistar Kyoto rats (WKY), and compared with data obtained from radioligand binding assays. Contractile responses induced in longitudinal and circular muscle layers by the alpha-adrenoceptor agonist noradrenaline (NA) and by barium chloride were recorded as described previously. in both muscle layers the maximal effects induced by NA, but not by BaCl2, were significantly greater in SHR. As a consequence, the relative responsiveness ratio (rho) for the alpha-adrenoceptor was also larger for SHR than for WKY. NA-induced contractions of both muscle layers were competitively antagonized by indoramine. the pA2 values for indoramine and pD2 values for NA were the same in SHR and WKY, indicating that alpha-adrenoceptor affinity was not changed in SHR. Additionally, binding studies with thc alpha-adrenoceptor ligand [H-3]WB4101 revealed that B(max) values were greater in the vas deferens of SHR, whereas K(d) values were not significantly different from those of WKY controls. in summary, although differences could not be detected for affinity-related parameters, a greater density of alpha-adrenoceptors was shown for SHR in receptor binding studies and this was corroborated by functional studies.
- ItemSomente MetadadadosLOW DIHYDROPYRIDINE RECEPTOR DENSITY IN VASA DEFERENTIA OF CASTRATED RATS(Stockton Press, 1992-02-01) Castillo, CJF; Lafayette, Simone Sette Lopes [UNIFESP]; Caricati-Neto, Afonso [UNIFESP]; Sette, Mario [UNIFESP]; Jurkiewicz, Neide Hyppolito [UNIFESP]; Garcia, Antonio G.; Jurkiewicz, Aron [UNIFESP].; Universidade Federal de São Paulo (UNIFESP); UNIV AUTONOMA MADRIDRadioligand binding studies in crude membrane preparations of vasa deferentia of normal rats, with the 1,4-dihydropyridine (+)-[H-3]-PN200-110 (isradipine) showed typical saturation isotherms. The binding exhibited a K(D) of 259 +/- 60 pM and B(max) of 144 +/- 20 fmol mg-1 protein. The low K(D) and the stereoselective displacement of (+)-[H-3]-PN200-110 binding by (+)- and (-)-PN200-110 and by nifedipine suggests that these tissues contain dihydropyridine receptors probably coupled to voltage-sensitive, L-type calcium channels. In membrane preparations from vasa deferentia from rats castrated 30 days previously the maximum specific binding was 25 +/- 10 fmol mg-1 protein, representing only 11% of total binding; thus, the calculation of reliable K(D) values was not feasible. These findings suggest that a testicular hormone, possibly testosterone, plays an important role in the regulation of dihydropyridine-sensitive, voltage-dependent calcium channels in the rat vas deferens.